fix in RooMinimizer the setting of limits on parameters in case of half-intervals [a, +INF] or [ -INF,b]
The parameters were in that case considered free or in same case (when calling minimize() a second time) set with lower=upper limit = 0  which was causing an assert in Minuit2

In case of TMinuit, half-intervals are not supported by transpormations, use then a large lower/upper bound value (not too large 
to avoid an error inside TMinuit)


git-svn-id: https://root.cern.ch/svn/root/trunk@48271 27541ba8-7e3a-0410-8455-c3a389f83636